The present invention relates to a downhole tool. In particular, but not exclusively, the present invention relates to a downhole tool for generating a longitudinal mechanical load.
A variety of different downhole tools are used in the oil and gas exploration and production industry. Existing downhole tools used for generating longitudinally directed mechanical loads, such as impact hammers, are designed primarily for the installation and/or retrieval of downhole assemblies, for example, nipples. Such existing hammers tend to be either structurally very simple or very complicated, with a large number of co-operating moving parts.
An example of a hammer of the structurally simple type is the “Plotsky” type hammer, which makes use of fluid swirls to develop a hammer action. In the Plotsky hammer, a fluid swirl is generated downstream of a nozzle in a fluid flow path. When the swirl breaks up, the fluid velocity decreases, causing an increase in the fluid pressure, which moves a piston in a percussive hammer action as the swirl builds up and breaks repeatedly. However, this results in poor performance of the hammer and, the fluid swirl is difficult to control.
Disadvantages associated with structurally complex hammers include that the hammers are difficult and expensive to manufacture, assemble and maintain.
Further types of downhole tools used for generating a longitudinally directed mechanical load include “fishing tools”. Fishing tools are used to recover downhole tools or strings of tubing which have become inadvertently stuck in a borehole and which cannot be removed by conventional means. Fishing tools are designed to latch onto the stuck tool or string and the fishing tool is then pulled from surface to dislodge the stuck tool or string and carry it to surface. In extreme circumstances where a fishing procedure fails, it is necessary to drill or mill the tool or string out of the borehole to re-open the hole.
The prior art devices exhibit various disadvantages, and the present invention now obviates or mitigates at least one of those disadvantages.